Over the past decade, numerous publications highlighted the medical role of hydrogen sulfide (H2S) for therapeutic applications and early diagnostics, traced in medical breath analysis e.g. with the “electronic nose” approach. It was shown that abnormal endogenous H2S concentration levels in exhaled breath samples can be linked to airway inflammation in asthma patients, and hence H2S functions as a potent biomarker.
In this work, we investigate the catalytic effects of gold (Au) and platinum (Pt) nanoparticle layer deposition on highly sensitive zinc oxide (ZnO) nanowires (NW) used for selective H2S detection in the sub-ppm region. High quality pristine ZnO NWs are grown by high temperature chemical vapor deposition (CVD) and vapor liquid solid growth (VLS) on silicon with a thin Au layer acting as a growth catalyst. The surface modification of pristine ZnO NWs was modified by systematical magnetron sputtering of discontinuous Au and Pt nanoparticle layers of 1 – 6 nm thickness. Resistive gas sensors based on the gas sensing mechanism of a chemical field effect transistor (ChemFET) with open gate, which is formed by hundreds of parallel aligned pristine, Au modified or Pt modified ZnO NWs, were measured towards H2S diluted in dry nitrogen (N2) or in dry synthetic air at room temperature. Gas sensing results allow for a first understanding of largely improved signal-to-noise ratio and response due to the catalytic effects of metal deposition on ZnO NW surface. Controlled application of optimized ZnO NW growth and metal catalyst deposition show a clear enhancement of response towards 1 ppm H2S from initial 15 % with pristine ZnO to 5000 % with ZnO after 5 nm Au deposition and hence greatly lower the limit of detection.